There has been considerable interest in recent years in developing high energy density batteries with lithium containing anodes. Lithium metal is particularly attractive as the anode of electrochemical cells because of its extremely light weight and high energy density, compared, for example, to anodes, such as lithium intercalated carbon anodes, where the presence of non-electroactive materials increases weight and volume of the anode, and thereby reduces the energy density of the cells, and to other electrochemical systems with, for example, nickel or cadmium anodes. These features are highly desirable for batteries for portable electronic devices such as cellular phones and laptop computers, as well as electric vehicles, military, and aerospace applications, where low weight is important.
Several types of cathode materials for lithium-anode batteries are known, and include cathode materials comprising sulfur-sulfur bonds, wherein high energy capacity and rechargeability are achieved from the electrochemical cleavage (via reduction) and reformation (via oxidation) of the sulfur-sulfur bonds. Sulfur-containing cathode materials, having sulfur-sulfur bonds, for use in electrochemical cells having lithium or sodium anodes, include elemental sulfur, organosulfur, and carbon-sulfur compositions.
During discharge of batteries that include a lithium anode and a sulfur-containing cathode, polysulfides form at the cathode of the batteries. Certain higher, soluble polysulfides may migrate to the anode and react with the anode, causing a reduction in battery performance. For example, the battery may exhibit self discharge, due to the presence of a redox shuttle mechanism, including the higher polysulfides. These polysulfides diffuse through the electrolyte to the anode where they are reduced to lower polysulfides that, in turn, diffuse back through the electrolyte to the cathode to be oxidized to higher polysulfides. This redox shuttle causes a continuous current flow in the cell, resulting in a depletion of the cell's stored capacity.
Accordingly, lithium-anode batteries with reduced self discharge are desired. In addition, it is generally desirable to have electrochemical cells with improved performance and properties, such as one or more of: the ability to fully charge, high utilization, high charge-discharge efficiency, and overcharge protection.